Chudobait

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Chudobait
Chudobaite.jpg
White chudobaite crystals from the Torrecillas Mine, Salar Grande, Iquique , Región de Tarapacá, Chile
General and classification
chemical formula
  • (Na, K) (Mg, Zn) 2 H [AsO 4 ] 2 • 4H 2 O
  • (Mg, Zn) 5 H 2 [AsO 4 ] 4 · 10H 2 O
  • (Mg, Zn) 5 (H 2 O) 8 (AsO 3 OH) 2 (AsO 4 ) 2 · 2H 2 O
  • (Mg, Zn) 5 [AsO 3 OH | AsO 4 ] 2 • (8 + 2) H 2 O
  • (Mg, Zn) 5 (AsO 4 ) 2 (AsO 3 OH) 2 · 10H 2 O
Mineral class
(and possibly department) 		Phosphates, arsenates and vanadates
System no. to Strunz
and to Dana 		8.CE.05 ( 8th edition : VII / C.14)
39.02.06.01
Similar minerals Spodumene var. Kunzite
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic pinacoidal; 1
Space group P 1 (No. 2)Template: room group / 2
Lattice parameters a  = 7.944  Å ; b  = 10.691 Å; c  = 6.770 Å,
α  = 80.97 °; β  = 84.20 °; γ  = 81.85 °
Formula units Z  = 1
Frequent crystal faces {100}, {010}, {001}
Physical Properties
Mohs hardness 2.5 to 3
Density (g / cm 3 ) 2.94 (measured); 2.93 (calculated)
Cleavage very good after b {010} and good after a {100}
colour pink, white, colorless
Line color probably white with a pale pink tinge
transparency transparent
shine "Medium to good gloss", "glass gloss"
Crystal optics
Refractive indices n α  = 1.583
n β  = ≈ 1.608
n γ  = 1.633
Birefringence δ = 0.05
Optical character biaxial negative
Axis angle 2V = 79 ° (measured) 88 ° (calculated)
Other properties
Chemical behavior Soluble in HCl, yellow precipitate with ammonium molybdate

Chudobaite is a very rare mineral from the mineral class of " phosphates , arsenates and vanadates ". It crystallizes in the triclinic crystal system with the chemical composition (Mg, Zn) 5 (AsO 4 ) 2 (AsO 3 OH) 2 · 10H 2 O and is chemically a water-containing magnesium - zinc - arsenate . The magnesium and zinc ions indicated in round brackets can represent each other in the formula ( substitution , diadochie), but are always in the same proportion to the other components of the mineral.

Chudobait develops isometric, large-area crystals up to 5 mm in size, the most recent of which are konichalcite, cuproadamine and zinc olivenite that grew up and in.

Etymology and history

Hugo Strunz, who collected the mineral in 1957 on the 1000 m level of the Tsumeb mine in SW Africa, is considered the discoverer of Chudobait. Corresponding investigations led to the determination of the presence of a new mineral, which Hugo Strunz could describe as Chudobait a short time later, in 1960 . The mineral was named after the German mineralogist and petrologist and rector of the Rheinische Friedrich-Wilhelms University in Bonn, Professor Karl Franz Johann Chudoba (1898–1976). Chudoba was the author of the Gemstone Study Manual and also editor of the supplementary volumes II to IV of Carl Hintze's Manual of Mineralogy .

Type material of the mineral is obtained at the Technical University of Berlin (Holotype and Cotyp, collection no. 86/95 and 86/66 at location 33-3) and at the École nationale supérieure des mines (ENSM, Cotyp) in Paris, France and on National Museum of Natural History (NMNH) in Washington, DC, USA (Collection No. 162628).

classification

Already in the outdated 8th edition of the mineral classification according to Strunz , the Chudobait belonged to the department of “Water-containing phosphates, arsenates and vanadates without foreign anions ”, where together with Hannayit the “Hannayit-Chudobait-Gruppe” with the system no. VII / C.14 and the other members Dittmarit, Schertelit , Stercorit , Taranakit formed.

In the last revised and updated Lapis mineral directory by Stefan Weiß in 2018 , which, out of consideration for private collectors and institutional collections, is still based on this classic system of Karl Hugo Strunz , the mineral was given the system and mineral number. VII / C.06-40 . In the "Lapis Classification" This also corresponds to the department "Water-containing phosphates, without foreign anions" (small and medium-sized cations: Be and Al-Mn-Fe-Cu-Zn-Mg) where Chudobait with Geigerit , Geminit , Hloušekit , Klajit , Kobaltkoritnigit , Koritnigit , Lindackerit , Magnesiokoritnigit , Ondrusit , Pradetit , Pushcharovskit , Rollandit , Slavkovit , Trichalcit , Veselovskyit and Yvonit form an independent but unnamed group.

The 9th edition of Strunz's mineral systematics, valid since 2001 and updated by the International Mineralogical Association (IMA) until 2009, also assigns chudobait to the category of “phosphates, etc. without additional anions; with H 2 O “. However, this is further subdivided according to the relative size of the cations involved and the molar ratio of the phosphate, arsenate or vanadate complex to the water of crystallization contained , so that the mineral is classified in the sub-section “With only medium-sized cations; RO 4  : H 2 O ≤ 1: 2.5 "is to be found, where it is named after the" Chudobait group "with the system no. 8.CE.05 and the only other member Geigerit.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the chudobait to the class of "phosphates, arsenates and vanadates", but there in the category of "water-containing acidic phosphates, etc.". Here he is to be found as the only member in the unnamed group 39.02.06 within the subdivision of " Hydrous acidic phosphates etc., H 2 (AB) 5 (XO 4 ) 4 × x (H 2 O) ".

Chemism

According to the original analysis, chudobaite had the measured composition (Na 0.74 K 0.19 Ca 0.08 ) Σ = 1.01 (Mg 1.37 Zn 0.65 Cu 0.01 Mn 0.13 ) Σ = 2, 16 H 0.66 [AsO 4 ] 1.99 • 4H 2 O, which was idealized to (Na, K) (Mg, Zn) 2 H [AsO 4 ] 2 • 4H 2 O. According to more recent information, the sodium , potassium and calcium contents are probably due to impurities, as they no longer appear in the formulas given there. A simplified formula is given for Chudobait with (Mg, Zn) 5 (AsO 4 ) 2 (AsO 3 OH) 2 · 10H 2 O, the contents of 12.43% ZnO, 15.82% MgO, 50.13% As 2 O 5 and 21.62% H 2 O requires.

Chudobaite is the magnesium / zinc-dominant analogue of the manganese-dominated geigerite.

Crystal structure

Chudobaite crystallizes in the triclinic crystal system in the space group P 1 (space group no. 2) with the lattice parameters a  = 7.944  Å ; b  = 10.691 Å; c  = 6.770 Å; α = 80.97 °; β = 84.20 ° and γ = 81.85 ° and one formula unit per unit cell . Template: room group / 2

The crystal structure of the Chudobait builds up parallel (010) (best cleavability!) From layers with four (Mg, Zn) O 6 - octahedra , which are connected to each other via edges and to the AsO 4 - tetrahedra via corners. The layers are held together by a fifth (centrosymmetrical) (Mg, Zn) O 6 octahedron and by water of crystallization molecules. As in all minerals of the chudobaite group, the M [6] octahedra in the chudobaite are linked to the AsO 4 and AsO 3 OH tetrahedra via common corners and form a three-dimensional framework.

properties

Drawing of a chudobait crystal from the Tsumeb mine

morphology

Chudobait forms isometric, large-area crystals up to 5 mm in size, whereby the pinacoids {100}, {010} and {001} are the crystal forms that determine the costume . {110}, { 1 20}, { 1 80}, {101}, { 1 84} and probably also {186} occur with blunt edges and corners , the latter crystal form, however, with strongly rounded edges (cf. the illustration opposite) .

physical and chemical properties

The crystals of the Chudobaite from Tsumeb are pink and show a similar color to the spodumene variety Kunzite. Colorless to white crystals are also described. The color of the line is not specified, but the powder color of the pink crystals should be white with a slight pink cast, while that of the white crystals is also white. The surfaces of the clear, transparent crystals have a “medium to good gloss ”, which is also described as glass gloss.

The mineral has two different fissile properties . It splits very well for b {010} and well for a {100}. With a Mohs hardness of 2.5 to 3, chudobaite is one of the medium-hard minerals that are somewhat easier to scratch with a copper coin than the reference mineral calcite . The measured density of the mineral is 2.94 g / cm³, its calculated density is 2.93 g / cm³. It was already pointed out in the original publication that chudobait does not fluoresce in the long or short-wave UV range and has no pyroelectricity or piezoelectricity either .

Education and Locations

As a very rare mineral formation, Chudobait could only be described from a few localities. So far (as of 2016) only two sites are known. The type locality is the world-famous Cu-Pb-Zn-Ag-Ge-Cd deposit of the "Tsumeb Mine" (Tsumcorp Mine) in Tsumeb , Oshikoto region , Namibia , where Chudobait was first found on the 1000 m level. It represents the most recent formation and was found grown up and in in yellow-green konichalcite, blue-green cuproadamine and dark olive-green, very shiny zinc olivenite, all minerals macroscopically crystallized idiomorphically and not altered. The ore matrix consists of coarse chalcosine and bornite.

A second chudobait discovery was only made in the Tsumeb Mine decades later. Here, colorless, very flat chudobaite crystals had grown together to form a 2 × 2 cm large aggregate, which was almost entirely in chalcosine.

Chudobait was identified a third time in Tsumeb in 1993 in connection with the last large cuproadamin find successful on the 44th floor. Here, both tiny, colorless crystals approx. 1 mm in size on ferrilotharmeyerite and white, skeletal cores in cuproadamine as chudobaite were determined.

Chudobait is a typical secondary mineral and (lower) formed in the second oxidation zone in dolomite stones seated hydrothermal polymetallic ore deposit Tsumeb from the sulfidic and arsenidischen Primärerzmineralen. It was formed from weakly acidic aqueous solutions at around 40 ° C and at around 1000 m water pressure. The arsenate was formed by the oxidation of arsenide ores, probably tennantite , the zinc probably arose from sphalerite , magnesium, calcium and perhaps also manganese from the dolomitic side rock, sodium and potassium from the feldspars of the pseudoaplites.

In addition to the Tsumeb mine Chudobait is still from the Mina Torrecillas, the type locality for seven minerals ( Canutit , Chongit , Gajardoit , Juansilvait , Leverettit , Magnesiokoritnigit and Torrecillasit ), in the district of Salar Grande in the province of El Tamarugal (former province of Iquique ), Región de Tarapacá , Chile , known. Here it is also a secondary alteration mineral and is accompanied by magnesiocorite nigite , anhydrite , halite , lavendulan , quartz and scorodite .

use

Due to its rarity, chudobait is only of interest to the mineral collector.

See also

literature

  • Rainer Dorner, Kurt Weber: The crystal structure of Chudobait, (Mg, Zn) 5 H 2 [AsO 4 ] 4 • 10H 2 O . In: The natural sciences . tape 63 , no. 5 , 1976, p. 243 , doi : 10.1007 / BF00610915 .
  • Hugo Strunz : Chudobaite, a new mineral from Tsumeb . In: New Yearbook Mineralogy, monthly books . 1960, p. 1-7 .
  • Chudobaite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 65 kB ; accessed on June 2, 2019]).

Web links

Individual evidence

  1. ↑ a b c d e f g h i j k l m n o p q r s t u v Hugo Strunz : Chudobaite, a new mineral from Tsumeb . In: New Yearbook Mineralogy, monthly books . 1960, p.  1-7 .
  2. ↑ a b c Rainer Dorner, Kurt Weber: The crystal structure of Chudobait, (Mg, Zn) 5 H 2 [AsO 4 ] 4 • 10H 2 O . In: The natural sciences . tape 63 , no. 5 , 1976, p. 243 , doi : 10.1007 / BF00610915 .
  3. ↑ a b Stefan Graeser, Hans Schwander, Riccardo Bianchi, Tullio Pilati, Carlo Maria Gramaccioli: Geigerite, the manganese analogue of chudobaite: Its description and crystal structure . In: American Mineralogist . tape 74 , 1989, pp. 676-684 (English).
  4. ↑ a b c d Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  478 (English).
  5. ↑ a b c d e f g h i Chudobaite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 65  kB ; accessed on June 2, 2019]).
  6. ^ A b David Barthelmy: Chudobaite Mineral Data. In: webmineral.com. Retrieved June 2, 2019 .
  7. ↑ Chudobaite. In: mindat.org. Hudson Institute of Mineralogy, accessed June 2, 2019 .
  8. ↑ Type mineral catalog of the University of Hamburg: Storage of the type material for Chudobait under catalog no. 86/66 / 33-3 and 86/65 / 33-3
  9. ↑ Catalog of Type Mineral Specimens - C. (PDF 130 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed June 2, 2019 .
  10. ↑ Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 6th completely revised and supplemented edition. Weise, Munich 2014, ISBN 978-3-921656-80-8 .
  11. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed April 25, 2019 .
  12. ↑ Rainer Dorner: The crystal structure of Chudobaits, Mg (Mg, Zn) 4 [(H 2 O) 8 | (HOAsO 3 ) 2 | (AsO 4 ) 2 ] · 2H 2 O . Technical University, Berlin 1976 (dissertation, Department 16 - Mining and Geosciences).
  13. ^ A b c Georg Gebhard: Tsumeb: A Unique Mineral Locality . 1st edition. GG Publishing, Grossenseifen 1999, ISBN 978-3-925322-03-7 , pp. 258-259 (English).
  14. ↑ Localities for Chudobaite. In: mindat.org. Hudson Institute of Mineralogy, accessed June 2, 2019 .
  15. ↑ Find location list for Chudobait at the Mineralienatlas and at Mindat
  16. ^ Anthony R. Kampf, Barbara P. Nash, Maurizio Dini, Arturo A. Molina Donoso: Magnesiokoritnigite, Mg (AsO 3 OH) H 2 O, from the Torrecillas mine, Iquique Province, Chile: the Mg-analogue of koritnigite . In: Mineralogical Magazine . tape 77 , no. 8 , 2013, p. 3081–3092 , doi : 10.1180 / minmag.2013.077.8.03 (English).